Extruder assemblies for injection moulding machines include piston screw that both reciprocate and rotate and includes a screw point at its leading end. The piston screw moves forward to inject melt and then retracts to take on new molten material to repeat the process.
Screw point that are currently being used generally have larger cross sections than screw points previously used. This increase results in an increase in the axial forces which are more difficult to overcome and also the response times are longer. This causes the material temperature to rise within the plasticizing screw, with attendant degradation of the material and losses in the injectable volume. The result of which is defects of the molded objects, which must then be rejected. In addition, the greater the axial forces, the higher the temperature will become and the greater the friction wear on the parts will be.